Electron beam gun

Abstract

Electron guns are disclosed that produce low-brightness and high-emittance electron beams that are suitable for use in an electron-beam reduction-lithography apparatus. A preferred embodiment comprises a cathode, a Wehnelt electrode, an anode, and at least one control electrode placed between the cathode and the anode. Each of these components defines a spherical surface all having a common center point and all thus being concentric with one another. During operation, the anode has a grounded electrical potential while the cathode and the Wehnelt electrode each have a potential of about -100 KV. If the applied voltage to the control electrode is adjusted within a range of -99 to -90 KV, the brightness can be controlled to within a range of 1×10 3 to 2×10 4 A/cm 2 .sr.

What is claimed is: 
     
       1. An electron gun for reducing projection-microlithography system, the electron gun comprising on an optical axis: (a) a cathode comprising a planar or spherically concave electron-emission surface, the cathode being cylindrical relative to the optical axis;   (b) an anode spaced from said cathode along the optical axis;   (c) a Wehnelt electrode having a proximal portion proximal to the cathode and disposed around the cathode and having a distal portion between cathode and the anode and;   (d) a control electrode situated between the cathode and the anode, the anode being structured and arranged so as to be electrically grounded during operation of the electron gun, the Wehnelt electrode being structured and arranged so as to have an electric potential, during operation of the electron gun, which potential tends to push electrons, in an electron beam emitted from the cathode, toward the optical axis.   
     
     
       2. The electron gun of claim 1, wherein the control electrode comprises a spherical portion rotationally about the optical axis and having a curvature radius extending from a center point located on the optical axis. 
     
     
       3. The electron gun of claim 2, wherein the anode has a spherical portion symmetrical about the optical axis and having center of curvature extending from the center point. 
     
     
       4. The electron gun of claim 3, wherein the electron-emission surface is spherically concave with a curvature radius extending from the center point. 
     
     
       5. The electron gun of claim 4, wherein the anode and the control electrode have respective curvature radii, the curvature radius of the control electrode being midway between the curvature radius of the electron-emission surface and the curvature radius of the anode. 
     
     
       6. The electron gun of claim 1, wherein: the electron-emission surface is planar, and   the control electrode and the anode each have respective spherical portions symmetrical about the optical axis and having a single center point located on the optical axis.   
     
     
       7. The electron gun of claim 1, wherein an angle between the Wehnelt electrode and an edge of a beam envelope of an electron beam emitted from the cathode is 70-85°. 
     
     
       8. The electron gun of claim 7, wherein: the electron-emission surface is spherically concave with a curvature radius extending from a center point on the optical axis; and   the electron-emission surface of the cathode defines an edge that is radially symmetrical about the optical axis, the edge being at a half angle, between the optical axis and a line extending from the edge to the center point, of 5° or less.   
     
     
       9. The electron gun of claim 8, wherein: the control electrode comprises a spherical portion symmetrical about the optical axis and having a center at the center point, the spherical portion of the control electrode defining a half angle φ 2  relative to the center point and situated between the optical axis and a portion of the spherical portion located farthest from the optical axis;   the anode has a spherical portion symmetrical about the optical axis and having center of curvature at the center point, the spherical portion of the anode defining a half angle φ 1  relative to the center point and situated between the optical axis and a portion of the spherical portion located farthest from the optical axis; and   the larger of φ 1  and φ 2  being 80° or greater.   
     
     
       10. The electron gun of claim 1, wherein during operation the anode is electrically grounded, the Wehnelt electrode has an electric potential and the cathode has an electric potential that is the same as the electric potential of the Wehnelt electrode, wherein changing the electric potential of the control electrode controls a brightness of an electron beam produced by the electron gun. 
     
     
       11. The electron gun of claim 1, wherein: the electron-emission surface is spherically concave with a curvature radius extending from a center point located on the optical axis;   the anode comprises a spherical portion symmetrical about the optical axis and having center of curvature at the center point; and   a ratio of the curvature radius of the electron-emission surface and the curvature radius of the anode is at least 5.   
     
     
       12. The electron gun of claim 1, further comprising a housing adapted to have an electrically grounded potential during operation of the electron gun. 
     
     
       13. The electron gun of claim 12, wherein the electron beam emitted from the electron-emission surface propagates along a beam envelope, the electron gun further comprising an electrode that shields the beam envelope from the electrically grounded potential of the housing. 
     
     
       14. The electron gun of claim 1, wherein the control electrode is structured and arranged so as to be able to change the electric field at the electron emission surface of the cathode. 
     
     
       15. The electron gun of claim 1, wherein the control electrode is structured and arranged such that changing the potential of the control electrode during operation of the electron gun controls the brightness of an electron beam produced by the electron gun. 
     
     
       16. The electron gun of claim 1, wherein the control electrode and the anode each have a respective spherical portion symmetrical about the optical axis, each respective spherical portion having a curvature radius about a center point located on the optical axis. 
     
     
       17. The electron gun of claim 1, wherein said electrodes from equipotential surfaces for allowing, during operation of the electron gun, a large emittance along a beam envelope traversed by an electron beam during operation of the electron gun. 
     
     
       18. An electron gun, comprising on an optical axis: (a) a cathode comprising a planar or spherically concave electron-emission surface;   (b) an anode spaced from said cathode along the optical axis;   (c) a Wehnelt electrode having a proximal portion proximal to the cathode and disposed around the cathode and having a distal portion between cathode and the anode; and   (d) multiple control electrodes situated between the Wehnelt electrode and the anode, wherein, during operation of the electron gun, an electric field produced between the cathode and the anode is controlled by the control electrodes.   
     
     
       19. The electron gun of claim 18, wherein each of the control electrodes comprises a spherical portion symmetrical about the optical axis and situated adjacent the optical axis, each spherical portion defines an aperture concentric with the optical axis; and   each spherical portion has a respective curvature radius extending from a single center point situated on the optical axis.   
     
     
       20. The electron gun of claim 19, wherein the anode comprises a spherical portion symmetrical about the optical axis and situated adjacent the optical axis, the spherical portion having a curvature radius extending from the center point. 
     
     
       21. The electron gun of claim 18, wherein the control electrodes are interconnected by electrical resistors so as to allow a single power supply to be used to apply electrical power to the control electrodes and the anode. 
     
     
       22. The electron gun of claim 20, wherein: the spherical portions of adjacent control electrodes are separated from each other by a respective radial distance;   the anode and the adjacent control electrode are separated from each other by a respective radial distance; and   each of the radial distances between the anode and the adjacent control electrode and between adjacent control electrodes being shorter than a length of an arc, concentric with said spherical surfaces, between the optical axis and a location on the respective anode and control electrodes where the respective spherical portion ends farthest away from the optical axis.   
     
     
       23. The electron gun of claim 20, wherein an equipotential surface is formed, during operation, in a region adjoining the cathode, the equipotential surface being shaped to cancel out a space-charge effect otherwise acting on an electron beam propagating from the electron-emission surface. 
     
     
       24. The electron gun of claim 14, wherein the control electrodes are structured and arranged such that changing the potential of the control electrodes, during operation of the electron gun, controls the brightness of an electron beam produced by the electron gun. 
     
     
       25. The electron gun of claim 14, wherein the control electrodes and the anode each comprise respective spherical portions symmetrical about the optical axis and situated adjacent the optical axis, the respective spherical portions each having a curvature radius about a center point on the optical axis.